Recently, as one of cancer treatments, a minimally invasive radiation treatment has attracted attention. The treatment applies less load on a human body and can maintain the quality of life at a high level after the treatment. Particularly, a particle beam therapy system using a charged particle beam such as protons or carbon accelerated by an accelerator such as a synchrotron, a cyclotron, or a linear accelerator provides high dose concentration to an affected part and has been expected as a promising system.
In case of irradiating a patient with a beam accelerated by the accelerator, as a unit to realize improvement of the dose concentration to the affected part and reduction of an irradiation dose to vital organs, irradiation using a rotating gantry which can irradiate with a particle beam from an arbitrary direction is effective. In order to achieve the above irradiation, it is necessary to bend charged particles. However, a magnet tends to increase in size so as to bend a high energy proton or heavier ions such as helium and carbon to obtain a desired irradiation field size. Also, demands for enlarging the irradiation available range tend to increase, and this causes a further increase in size of the magnet. Therefore, it is desired to realize a compact and lightweight rotating gantry, with which a large irradiation field can be formed.